Radar detection for wireless communication devices

ABSTRACT

A method and apparatus for detecting radar signals in single and multiple (extension) channel wireless network frequencies uses spectral and DC analysis. Spectral images produced through a Fast Fourier transform may be captured and analyzed to determine if any radar signals may be present within the selected wireless network frequencies. A plurality of spectral images may also be analyzed to determine if frequency shifting radar signals are present as well. DC analysis of the power contained at the wireless carrier frequencies may detect radar signals that may be centered near those frequencies.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/187,239, entitled “Radar Detection For Wireless CommunicationDevices” filed Aug. 6, 2008 which claims priority of U.S. ProvisionalPatent Application 60/954,559, entitled “Radar Detection For WirelessCommunication Devices” filed Aug. 7, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to wireless localarea networks and more specifically to detecting radar signals withinwireless local area networks.

2. Description of the Related Art

Wireless Local Area Network (WLAN) devices must coexist with radarsignals in the 5 GHz frequency bands. The general requirement is thatWLAN devices should avoid operating on frequencies where radar signalshave been detected.

A frequency band may be divided into one or more channels. The bands andchannels for one form of wireless communication may be defined by, forexample, the IEEE 802.11 family of standards. A WLAN transmittertypically transmits data through a channel to one or more WLANreceivers. A typical bandwidth of a channel is 20 MHz. Moreover, theIEEE 802.11 family of standards may also define how the data may beconfigured into data packets that typically include a preamble and apayload. The preamble may include training fields that typically precedethe payload in each data packet. The IEEE 802.11 family of standardsalso defines modulation schemes such as Orthogonal Frequency-DivisionMultiplexing (OFDM) that use closely spaced orthogonal sub-carriers tocarry the payload. Each orthogonal sub-carrier frequency is typicallyreferred to as a “bin”, data within each bin is typically encoded forOFDM modulation with a Fast Fourier transform (FFT), and the resultingreal (I) and imaginary (Q) parts of the FFT are transmitted.

The IEEE 802.11n draft standard describes how a WLAN transmitter maytransmit data through two channels instead of a single channel in orderto increase the overall effective bandwidth of a channel, i.e. a widerchannel may advantageously increase the data transfer rate. The twochannels are typically chosen from within a selected band such that theydo not overlap and are often referred to as a control channel and anextension channel. As in the single channel case, a preamble containingtraining fields precedes the payload transmission on both the controland the extension channels. The typical bandwidths of control andextension channels are the same as in the single channel case (20 MHz),which means the combined bandwidth is approximately 40 MHz.

If a radar signal is detected within a channel used for wirelesscommunications, many specifications (e.g. IEEE 802.11 family ofstandards) require that WLAN devices leave that channel and move to achannel that does not interfere with the radar signals. In the case of atwo-channel configuration, radar signals must be detected in bothchannels. Many radar signals in the 5 GHz spectrum typically includeperiodic bursts of radar pulses. The bursts typically have a period ofabout 1 ms and the pulse duration is typically between 1-5 us. There aremany known methods to detect such radar signals. For example, one methodmeasures the pulse duration and the pulse burst period and compares thatinformation against many known radar characteristics. Another methodsimply looks for the presence of a received signal above a thresholdduring a ten second start-up period. Yet another method compares theamount of power that appears in-band to the power that appearsout-of-band.

Some radar signals, however, have different characteristics. Forexample, other radar signals may have a wider pulse width between 50-100us, and an additional characteristic in which the frequency of the radarsignal varies in time causing the appearance of some radar signals tomove across frequency bins over time. These radar signals may appear asa noise spur or other type of signal interference making radar signaldetection difficult. Traditional radar detection methods, such as thosedescribed above, may not be effective in detecting some radar signals,particularly those that may change in frequency over time.

Radar signals may exist anywhere within a channel, in some instancesaligning with the carrier frequency of a selected channel. Typically,when a WLAN signal is brought down to baseband, the energy of thecarrier frequency is suppressed since it appears as a DC offset to thebaseband signal and, as such, does not have any modulation information.Thus, if a radar signal is aligned to the carrier frequency, then theradar signal may be difficult to detect. In the case of a two channelWLAN, a radar signal may align with the carrier frequency of thecombined control/extension channel. The carrier frequency energy isagain suppressed as in the single channel case. Thus, the two channelWLAN also has a radar detection problem.

Therefore, what is needed in the art is a method for detecting radarsignals, particularly radar signals that may have a frequency thatvaries in time and radar signals that may align with carrierfrequencies. This method should be applicable to both single andmultiple channel WLANs.

SUMMARY OF THE INVENTION

A method of detecting radar signals can include detecting an increase inpower in a received signal and, when no increase in power is detected,analyzing the DC component sizes of the received signal. Advantageously,if a detected DC component associated with a particular gain setting isgreater than a typical DC component associated with a similar gainsetting, then radar signals may be present within the selected channel.The method can also include determining whether a maximum power of thereceived signal is greater than a radar threshold when an increase inpower is detected. In one embodiment, the radar threshold can beprogrammable. FFT radar analysis can be performed when the maximum powerof the received signal is greater than the radar threshold, the power ofthe received signal is in-band, and a preamble is not detected in thereceived signal. Thus, radar is advantageously detectable based oneither analyzing the DC component sizes or performing FFT radaranalysis.

In one embodiment, the method can further include splitting the receivedsignal into multiple signals and for each signal determining whether thepower is in-band, detecting a preamble in the signal, and performing FFTradar analysis when the maximum power of the signal is greater than theradar threshold, the power is in-band, and a preamble is not detected inthe signal.

A wireless network device for implementing the above-described methodcan include an analog section, a digital section, and a processor. Thedigital section can include a DC removal unit for receiving an output ofthe analog section, an FFT unit for receiving an output of the DCremoval unit, a spectral analysis unit for receiving the output of theFFT unit, a first power measuring unit for receiving the output of theDC removal unit, a filter for receiving the output of the DC removalunit, and a second power measuring unit for receiving the output of thefilter. In this configuration, the processor can receive the output ofthe DC removal unit, the spectral analysis unit, the first powermeasuring unit, and the second power measuring unit. This configurationcan be used for a single channel wireless network device. In oneembodiment, the processor can include an averaging unit for receiving anoutput of the spectral analysis unit.

The digital section of another wireless network device can include a DCremoval unit for receiving an output of the analog section, an FFT unitfor receiving an output of the DC removal unit, a spectral analysis unitfor receiving the output of the FFT unit, a first power measuring unitfor receiving the output of the DC removal unit, a signal splitter forreceiving the output of the DC removal unit, a plurality of processingpaths for receiving an output of the signal splitter, and a processor.Each processing path can include a filter for receiving the output ofthe signal splitter and a power measuring unit for receiving the outputof the filter. Advantageously, the frequencies filtered by these filtersslightly overlap, thereby ensuring coverage of the complete bandwidthfor the in-band signal analysis. In this configuration, a processor canreceive the outputs of the DC removal unit, the spectral analysis unit,and each of the processing paths. This configuration can be used for amultiple channel wireless network device. In one embodiment, theprocessor can include an averaging unit for receiving an output of thespectral analysis unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a simplified diagram of a wireless network device.

FIG. 2 illustrates a more detailed diagram of a portion of the wirelessnetwork device of FIG. 1.

FIGS. 3A and 3B are graphs showing exemplary outputs of the FFT unit ofFIG. 2.

FIG. 4 illustrates a method for detecting radar signals, according tothe specification.

FIG. 5 illustrates a diagram of an alternative embodiment of a wirelessnetwork device.

DETAILED DESCRIPTION OF THE DRAWINGS

As described in further detail below, the presence of radar signalswithin wireless frequencies used by WLANs can be detected by analyzingspectral frequency data and by monitoring the power that is present inand near selected channels. The embodiments described herein may beapplied to both single and multiple channel configurations.

FIG. 1 is a simplified diagram of a wireless network device 100according to the specification. The wireless network device 100includes, without limitation, an antenna 105, an analog section 110, adigital section 120, a processor 130, and a data interface 140. Theantenna 105 is coupled to an input of the analog section 110. Radiofrequency (RF) signals that include WLAN communication signals arereceived by the antenna 105 and are provided to the analog section 110.The analog section 110 processes the RF signals by converting the RFsignals to digital baseband signals. The digital section 120 receivesthe digital baseband signals output by the analog section 110 andrecovers WLAN data from the digital baseband signals. The recovered WLANdata, which is output by the digital section 120, is provided to thedata interface 140 and is to other devices (not shown). The datainterface 140 outputs the WLAN data in a form accessible to a user. Theprocessor 130 is coupled to the analog section 110, the digital section120, and the data interface 140. The processor 130 may be a centralprocessing unit (CPU), a processing core, or some other device that mayread and execute software instructions or micro-code. The processor 130may control and configure the analog section 110, the digital section120, and a portion of the data interface 140.

FIG. 2 is a more detailed diagram of a portion of the wireless networkdevice 200 of FIG. 1. Specifically, the antenna 105, the analog section110, the digital section 120, and the processor 130 are shown in FIG. 2.Note that the data interface 140 of FIG. 1 has been omitted for clarity.

The analog section 110 includes, without limitation, a variable gainamplifier (VGA) 205, an analog-to-digital converter (ADC) 210, and anautomatic gain controller (AGC) 220. The antenna 105 is coupled to theinput of the VGA 205. RF signals received by the antenna 105 areprovided to the VGA 205. In one embodiment, the VGA 205 is a wideband,variable gain amplifier that may increase the signal strength of thereceived RF signal. The VGA 205 may also include devices, such as one ormore mixers, filters, and oscillators (not shown), to convert thereceived RF signal to an analog baseband signal. The analog basebandsignal produced by the VGA 205 is provided to the input of the ADC 210,which in turn converts the analog baseband signal to a digital basebandsignal. This digitized baseband signal of the ADC 210 is provided to theAGC 220 and to the digital section 120. The AGC 220 analyzes thisdigitized baseband signal and adjusts the gain of the VGA 205 so thatthe output of the ADC 210 is not limited by the upper or lower bounds ofthe ADC 210. The AGC 220 also may provide information about the gainsetting of the VGA 205 through a coupling to the processor 130. The gaininformation may be used to detect radar signals and is described belowin greater detail in conjunction with a DC removal unit 230.

In one embodiment, the AGC 220 may also detect preambles within datapackets and signal the processor 130 that such preambles are present. Asdescribed herein, the preambles are transmitted as part of each datapacket and, therefore, may indicate the presence of a valid data packet.The preamble information may be used to detect radar signals and isdescribed below in greater detail in conjunction with FIG. 4.

The digital section 120 includes, without limitation, the DC removalunit 230, a first power measuring unit 240, a filter 250, a second powermeasuring unit 260, a FFT unit 270, and a spectral analysis unit 280.The output of the ADC 210 is coupled to the input of the DC removal unit230. Baseband signals commonly include a DC component resulting from thecarrier frequency. As previously noted, a DC component included in thebaseband signal is removed prior to further processing. This is becausethe carrier frequency, which is the source of the DC component, containsno information, but instead adds only a DC component to the basebandsignal. However, in the case when a radar signal has the same frequencyas the carrier frequency, the presence of the radar signal may be hiddenby the DC removal process.

In accordance with one embodiment of a radar detection method, the DCremoval unit 230 determines the amount of DC present in the basebandsignal and removes the DC component. Advantageously, the DC componentsize may indicate the presence of radar signals in the wirelesscommunication channel, thus the size of the DC component is provided tothe processor 130.

In one embodiment, the processor 130 may construct a table that includestypical DC component sizes and their associated gain settings applied bythe AGC 220 to detect radar signals that may be centered on the carrierfrequency. Such data may be collected while the wireless network device200 is receiving transmitted data packets. After the table is built, ifthe processor detects a DC component associated with a particular gainsetting that is greater than the DC component stored in the tableassociated with a similar gain setting, then radar signals may bepresent within the selected channel.

The DC corrected digital baseband signal from the DC removal unit 230 isprovided to the first power measuring unit 240, the filter 250, and theFFT unit 270. The first power measuring unit 240 measures the powercontained in the DC corrected digital baseband signal. In oneembodiment, power is measured by adding the absolute values of the I andQ values in the DC corrected digital baseband signal. In an alternativeembodiment, power may be measured by adding the square of the I and Qvalues together. The first power measuring unit 240 provides a powermeasurement of the signals both in and near the selected channel. Thismeasure of power may indicate the presence of signals processed by theanalog section 120 as well as radar signals (described in greater detailin conjunction with FIG. 4).

The filter 250 filters the data from the DC removal unit 230 to limitthe data to a selected bandwidth and suppress out-of-band signals andnoise. In one embodiment, the filter 250 limits the signal to 20 MHz,which is the bandwidth of a single channel as described herein, and maybe implemented as a low pass filter. The output of the filter 250 iscoupled to the input of the second power measuring unit 260. The secondpower measuring unit 260 may function substantially similar to the firstpower measuring unit 240. However, in this case, the second powermeasuring unit 260 measures the power of the filtered digital basebandsignals output by the filter 250. The processor 130 may compare thepower measured by the first and second power measuring units 240 and260, respectively, to determine if radar signals are present within theselected channel. This is described in greater detail below inconjunction with FIG. 4.

Data from the output of the DC removal unit 230 is provided to the inputof the FFT unit 270. The FFT unit 270 typically performs an FFTcomputation on the data from the DC removal unit 230 to recover thepayload. The FFT unit 270 may also capture one or more spectral imagesto facilitate radar detection. The spectral analysis unit 280 analyzesthe spectral images from the FFT unit 270. The analysis is described ingreater detail in conjunction with FIGS. 3A and 3B. The data from thespectral analysis unit 280 is provided to the processor 130 and may beused to detect radar signals, which is described in greater detail inconjunction with FIG. 4.

Radar signals may be relatively narrower in bandwidth than a datapacket. One method for detecting radar signals analyzes the FFT outputof a selected channel and looks for output peaks that may correspond tonarrow-band radar signals.

FIG. 3A is a graph 300 showing an exemplary output of the FFT unit 270.As is well-known, OFDM modulation described by the IEEE 802.11 family ofstandards encodes data packets with sixty-four orthogonal carrierfrequencies (bins). Twelve of the sixty-four bins are typically not usedso that a guard band of six bins appears at the beginning and end of theOFDM packet. Thus, although there may be an FFT output point for each ofthe sixty-four bins, only bins 6 through 57 may have a non-zero FFTmagnitude (i.e., bins 0-5 and 58-63 are zero). In this exemplary graph,only four FFT output points are shown and the other sixty have been leftoff for clarity. Point 310 shows the FFT magnitude associated with bin6, point 315 is associated with bin 20, point 320 is associated with bin25 and point 325 is associated with bin 57.

Analysis of the FFT output may include assigning descriptors to each FFToutput point. In one embodiment, a four-bit descriptor is assigned toeach FFT output point and the descriptor may be provided by the spectralanalysis unit 280 of FIG. 2. The four-bit descriptor may be theconcatenation of a one-bit threshold indicator and a three-bit magnitudeindicator. The three-bit magnitude indicator may be used to describe themagnitude of a FFT output point relative to the output point with thelargest magnitude in the current FFT output such as the outputillustrated by graph 300. If the FFT output point exceeds a threshold,then the one-bit threshold indicator may be set. In one embodiment, thethreshold indicator bit may be the most significant bit of the four-bitdescriptor. The four-bit descriptors associated with FFT outputs may beanalyzed to determine if radar signals are present in the selectedchannel and more particularly if a narrow band, frequency hopping radarsignal is present.

In one embodiment, spectral analysis unit 280 may examine each outputpoint in an FFT output and determine which FFT output point has thelargest magnitude. The magnitude of the other output points in the FFToutput 300 may then be described with a three-bit number correspondingto the output magnitude relative to the output point with the largestmagnitude. Since three bits are used, (111) is the largest and (000) isthe smallest magnitude. For example, an FFT output point with thelargest magnitude may be assigned a three-bit magnitude descriptor of(111) whereas an output point that is approximately one-half themagnitude of the output point with the largest magnitude, may beassigned a three-bit magnitude descriptor of (100). Other bit widths maybe used to implement the magnitude descriptor to provide more or lessmagnitude resolution.

The spectral analysis unit 280 may also compare each of the FFT outputpoints to a threshold. If the magnitude of an FFT output point isgreater than the threshold, then the threshold indicator bit may be setto one. In FIG. 3A, an exemplary threshold 330 is shown on the graph300. Returning to our example, since point 315 is greater than thethreshold, the fourth bit of the associated descriptor is set. In oneembodiment, the threshold 330 may be used to determine whether anysignals are within the selected channel. For example, if groups of FFToutput points are greater than the threshold 330, then a narrow bandsignal, such as a radar signal may exist in the selected channel. On theother hand, if no FFT output points are greater than the threshold 330,then there may be no signals in the selected channel. If all of the FFToutput points are greater than the threshold 330, then a wide bandsignal may be present in the selected channel. Table 1 below lists theFFT output points, associated bin number and related four-bitdescriptors of graph 300.

TABLE 1 Descriptors for Output Points in FIG. 3A Point Bin Descriptor310 6 (0001) 315 20 (1111) 320 25 (0010) 325 57 (0001)

FIG. 3B is a graph 350 showing another exemplary output of the FFT unit270. Another exemplary threshold 380 is shown in graph 350. In thisexample, the threshold 380 may be similar to the threshold 330 shown ingraph 300. In some cases, the threshold may be relatively fixed in orderto track FFT output peaks. Other times, the threshold may be changed toadapt to different environments. For example, if there is enough noisein the channel making FFT output peak detection relatively difficult,then the threshold may be increased, decreasing noise sensitivity. Ingraph 350, FFT output point 360 illustrates the FFT output magnitudecorresponding to the FFT output at bin 6, point 365 corresponds to bin20, point 370 corresponds to bin 25 and point 375 corresponds to bin 57.As described in FIG. 3A, descriptors may be assigned to the FFT outputpoints by the spectral analysis unit 280. Table 2 below lists thepoints, associated bin number and related four-bit descriptors of graph350.

TABLE 2 Descriptors for Output Points in FIG. 3B Point Bin Descriptor360 6 (0001) 365 20 (0010) 370 25 (1111) 375 57 (0001)

Analysis of the FFT outputs may be used to determine if radar signalsmay be present in the selected channel. Certain narrow-band radarsignals may be relatively easy to discern from the FFT outputs.Narrow-band radar signals may appear as peaks in the FFT output. Anoutput peak may include one or more FFT output points. The descriptorsfor a particular FFT output may be examined to determine if narrow-bandradar signals are present. For example, FFT output point 315 located atbin 20 in FIG. 3A may correspond to an output peak due to a radarsignal. The peak may be located by analyzing the descriptors of the FFToutput points. The descriptors may be scanned by either hardware (suchas the spectral analysis unit 280), or by the processor 130 to locateFFT output peaks. In one embodiment, FFT output peaks may be located byreviewing the threshold indicator bit of the four-bit descriptor.

Analysis of two or more FFT outputs may be used to determine iffrequency hopping radar signals may be present in the selected channel.For example, let FIG. 3A be a first FFT output and FIG. 3B be a secondFFT output captured by the same wireless network device 200 a timeperiod after the first FFT output. The presence of similar FFT outputpeaks located at different bins in different FFT outputs may indicatethe presence of a frequency hopping radar signal in the selectedchannel. In one embodiment, the spectral analysis unit 280 mayadvantageously detect frequency hopping radar signals by scanning thedescriptors associated with two or more FFT outputs. In this example, anFFT peak may be observed at bin 20 in FIG. 3A and at bin 25 in FIG. 3B,which may indicate the presence of a frequency hopping radar signal inthe selected channel.

In one embodiment, the processor 130 can include an averaging unit 290that captures the results for each FFT period. In this embodiment,further analysis can be performed over multiple, consecutive FFTperiods. This averaging capability can advantageously improve therobustness of the analysis provided by processor 130.

FIG. 4 illustrates a method 400 for detecting radar signals, accordingto the specification. Persons skilled in the art will recognize that anysystem configured to perform the method steps in any order is within thescope of the invention.

Step 405 determines if there is an increase in power detected within thereceived signal. An increase in power may indicate the presence of aradar signal. In one embodiment, power in the received signal may bemeasured by the DC removal unit 230 and the power measurement unit 240of FIG. 2. If no increase in power is detected, step 417 determines DCcomponent sizes that are removed from the baseband signal and runs radaranalysis based on such DC component sizes. As described in FIG. 2, a DCcomponent that is larger than typical previously received DC componentsmay be caused by radar signals. In one embodiment, DC component sizesmay be determined by the DC removal unit 230 of FIG. 2 and analysis ofsuch DC component sizes may be performed by the processor 130. Themethod 400 then returns to step 405 for the next signal.

If a power increase is detected in step 405, then step 410 determines ifsuch power increase is greater than a radar power threshold. In oneembodiment, the radar power threshold is a programmable threshold thatmay be used to select power measurements that may be associated withradar signals. If the increase in power is not greater than the radarpower threshold, then the method returns to step 405. The powerthreshold may be set such that increases in measured power due to noiseevents advantageously do not result in radar signal detection.

If the increase in power is greater than the radar power threshold, thenstep 415 determines if the detected power is in-band (i.e., the detectedpower exists within the bandwidth of the selected channel). Because somewireless communication devices may receive signals beyond the wirelesscommunication channel, step 415 refines the power measurement of step405 by limiting the power measurement to in-band power. In oneembodiment, filter 250 may be used in conjunction with power measuringunit 260 to determine if the detected power is in-band.

If the detected power is not in-band, then the method returns to step405 for the next signal. If the detected power is in-band, then step 420determines if a preamble has been detected. The presence of the preambleusually indicates the presence of a valid wireless communication packet(and therefore the received signal is not a radar signal). In oneembodiment, the AGC 220 can inspect data from the ADC 210 and determineif the data from the ADC 210 includes a valid preamble. If a validpreamble is detected, then step 430 decodes the data packet. In oneembodiment, the data packet may be decoded with the FFT unit 270. If avalid preamble is not detected, then step 425 performs FFT analysis todetermine if radar signals are present in the wireless communicationchannel. The FFT analysis may include capturing the output of the FFTunit 270 and examining the descriptors associated with the output pointsas described in conjunction with FIGS. 3A and 3B.

The method 400 of FIG. 4 enables radar signals within a selected channelto be detected. Moreover, the FFT unit 270, which normally may be usedto decode data packets, may be advantageously used to generate thespectral image used in step 425; thus, a dedicated FFT unit is notrequired since the FFT unit 270 would be otherwise idle.

The wireless network device of FIG. 2 may detect radar signals presentin a single channel. When wireless data is sent through more than onechannel, such as through control and extension channels, radar signalsmay be detected with a similar wireless network device. Such a networkdevice is described below in FIG. 5.

FIG. 5 is a diagram of an alternative embodiment of a wireless networkdevice 500. The wireless network device 500 may be configured to receivedata packets simultaneously on a control and an extension channel asdescribed by the IEEE 802.11n draft standard. The wireless networkdevice 500 may also be configured to detect radar signals on both thecontrol and extension channels. The wireless network device 500includes, without limitation, an antenna 105, an analog section 110, adigital section 510, and a processor 130. The antenna 105, the analogsection 110 and the processor 130 function substantially similar to theantenna 105, analog section 110 and processor described in conjunctionwith FIG. 2. A data interface, such as data interface 140 in FIG. 1, mayalso be included with the wireless network device 500, but is not shownhere for clarity.

The digital section 510 includes a DC removal unit 550, an FFT unit 530,a spectral analysis unit 540, a signal splitter 520, a first, second andthird power measurement units 240, 260 a, and 260 b, respectively, and afirst and second filter 250 a and 250 b, respectively.

As with the wireless network device of FIG. 2, a digital baseband signalfrom the analog section 110 is provided to the DC removal unit 550 ofthe digital section 510. The DC removal unit 550 determines the size ofthe DC component present in the baseband signal and removes that DCcomponent. As described herein, the size of the DC component may be usedto determine the presence of radar signals, thus the size of the DCcomponent is provided to the processor 130. The carrier frequency for atwo channel (control and extension) system is typically located betweenthe control and extension channels. Thus, in this case, the DC removalunit 550 removes the DC component of the baseband signal located betweenthe control and extension channels. As described herein, the DCcomponent size may be used to determine the presence of radar signals inthe selected channel.

The processed digital baseband signal produced by the DC removal unit550 is coupled to the first power measurement unit 240, the signalsplitter 520, and the FFT unit 530. The first power measurement unit 240functions similarly to the power measurement unit 240 of FIG. 2 andmeasures the power in the processed digital signal (in combination withDC removal unit 550). This power measurement may be used to determine ifthere are any signals present in and near the control and/or extensionchannels.

The processed digital baseband signal can be divided into two signals bythe signal splitter 520. In one embodiment, a first signal may be thecontrol channel signal, and a second signal may be the extension channelsignal. The first divided signal is provided to the first filter 250 awhich removes out-of-band signal components similar to the filter 250 ofFIG. 2. The output of the first filter 250 a is provided to the secondpower measuring unit 260 a. The second power measuring unit 260 ameasures the power included in the control channel signal similar to thepower measuring unit 260 of FIG. 2. This power information is providedto the processor 130.

The second divided signal is provided to the input of the second filter250 b, which also removes out-of-band signal components (similar to thefilter 250 of FIG. 2). The output of the second filter 250 b is providedto the third power measuring unit 260 b. The third power-measuring unit260 b measures the power in the extension channel (similar to the powermeasuring unit 260 of FIG. 2). This power information is provided to theprocessor 130.

The processed digital baseband signal is also provided to the input ofthe FFT unit 530. The FFT unit 530 may be used to create spectral imagesof the combined control and extension channel. The spectral images arecoupled to the spectral analysis unit 540. This spectral image maydiffer from the spectral image described in conjunction with FIGS. 2 and3 because the bandwidth of the combined control and extension channel is40 MHz compared to 20 MHz bandwidth of a single channel. However, thesame analysis techniques may be applied as before. For example, thefour-bit descriptors may be assigned to FFT output points in the samemanner as described in FIGS. 3A and 3B.

The method 400 of FIG. 4 may be applied to the wireless network device500 with only a small modification. For example, because two channelsare being used, step 415 may be modified to check the in-band power forboth the control and extension channels. Thus, if power is detected inthe control or the extension channels, the method 400 proceeds to step420 to determine if preambles have been detected. On the other hand, ifpower is not detected in either the control or the extension channels,then the method 400 returns to step 405. The other steps of the method400 described in FIG. 4 may remain the same.

The FFT unit 530 may be configured to process data for a 40 MHz channel,which is the typical bandwidth required for a combined control andextension channel. In one embodiment, an additional processing path(receiving another output of signal splitter 520) may include a filter250 c and a power measuring unit 260 c. The filter 250 c can provide aslight overlap in frequencies between filters 250 a/250 c as well asbetween filters 250 b/250 c. This overlap can advantageously ensurecoverage of the complete bandwidth for the in-band signal analysisperformed by processor 130. Additionally, when analyzing the resultsfrom power measuring units 260 a, 260 b, and 260 c, processor 130 candetermine whether frequency hopping occurs between the processing paths(each processing path including a filter a power measuring unit). Notethat other embodiments may include any number of processing pathsdepending on the multiple frequency band being evaluated, the capabilityof the signal splitter, and the availability of filters.

Although illustrative embodiments of the invention have been describedin detail herein with reference to the accompanying figures, it is to beunderstood that the invention is not limited to those preciseembodiment. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed. As such, many modificationsand variations will be apparent. Accordingly, it is intended that thescope of the invention be defined by the following Claims and theirequivalents.

1. A method of detecting radar signals, the method comprising: detectingan increase in power in a received signal; analyzing DC component sizesof the received signal when no increase in power is detected;determining whether a maximum power of the received signal is greaterthan a radar threshold when an increase in power is detected;determining whether the power is in-band; detecting a preamble in thereceived signal; and performing FFT radar analysis when the maximumpower of the received signal is greater than the radar threshold, thepower is in-band, and a preamble is not detected in the received signal,wherein radar is detectable based on one of analyzing DC component sizesand performing FFT radar analysis.
 2. The method of claim 1, wherein theradar threshold is programmable.
 3. The method of claim 1, furtherincluding: splitting the received signal into multiple signals and foreach signal, determining whether the power is in-band; detecting apreamble in the signal; and performing FFT radar analysis when themaximum power of the signal is greater than the radar threshold, thepower is in-band, and a preamble is not detected in the signal.